Industrial laundries clean a variety of different articles which produce different effluent. In typical industrial laundries, two-thirds to three-quarters of the laundry will be relatively easily cleaned articles such as clothing, linen, bath towels, etc. The remaining quarter to one-third of the laundry will be substantially dirtier articles, such as shop towels, mop heads, and so on. The effluent from these dirtier articles is, of course, substantially different and typically high in oil content.
All of the effluent from the laundry, however, must meet the same environmental standards in terms of oil and grease (0 & G), total suspended solids (TSS), chemical oxygen demand (COD), biological oxygen demand (BOD), and POTW.
With the nonoily effluent produced from washing clothing and the like, relatively little treatment is required to meet these requirements. Generally, filtering the total suspended solids using a shaker screen produces an effluent which is suitable for disposal directly to a sanitary sewer. However, this treatment is not effective for an oily effluent produced by washing shop towels and the like. Typically, the oily effluent from washing shop towels can include 500 to about 5000 ppm of oil. This must be reduced to about 100 ppm.
The treatment of the oily effluent creates a significant problem because the detergent acts by emulsifying the oil in water. Basically that is the purpose of the detergent. To remove the oil, one must demulsify the detergent which presents an even greater problem.
All effluent from the laundry must be treated to remove suspended solids. All effluents must also pass through a common heat exchanger. Treating all effluents in the same manner to remove suspended oil, however, is very expensive. Treating a larger quantity of effluent drastically increases capital costs.